The fouling of heat transfer surfaces due to the deposition of slag and other constituents of fly ash is a major problem facing the operators of coal fired steam generators. Reduction of heat transfer coefficients on the outer surface of boiler tubes changes the heat distribution within the furnace and reduces overall boiler efficiency. Continued increase of the fouling will eventually reduce the units' generating capability. In addition, ash and slag deposition results in increased velocities and pressure drops in the convective regions of steam generators, thus potentially increasing erosion and auxiliary power consumption. Furthermore, this accumulation often accelerates metal corrosion because of the coatings' chemical composition.
In order to minimize the effect of slag deposition, soot blowers are employed at both the furnace wall and in the convective regions of the steam generator. These soot blowers direct controlled jets of high energy compressed air or superheated steam against the surfaces to mechanically remove the slag and ash deposits. Currently, soot blowers are either operated on a varying time-actuated cycle, or they are turned on manually based upon the operator's perception of the need to clean the furnace. Both of these methods are inadequate. Because the conditions of the furnace fluctuate widely, a time actuated sequence may or may not be effective in removing the slag and soot on the one hand or, if they are operated too frequently, unnecessary energy is expended. The same problems exist if there is manual operation based upon an operator's perception of the need to clean the furnace.
Several slag (ash) and heat flux monitors have been developed toward solving the problem of determining slag buildup and the measuring of heat flux in boiler furnaces. Typical of the ash monitoring systems is described in Trans. of the ASME I1. of Engr. for Power, Vol. 103, p. 532 (July 1981). An article describing a heat flux monitor appears in Int. J. Heat Mass Transfer, Vol 23, p. 1023 (1980). Both of these monitors (and others known in the art) utilize thermocouples for determining temperatures. None, however, provide for an active method of directly determining the surface condition of the monitor.
Accordingly, it is a principal object of the present invention to provide a means for directly monitoring the condition of heat transfer surfaces and activating a removal system only when such would be of significant benefit.
It is another object of the present invention to provide means for operating soot blowers and the like within furnaces only under absolutely needed conditions thereby reducing corrosion and erosion of the surfaces, and in particular, tube walls.
It is also an object of the present invention to provide a device for monitoring the effective heat transfer of a heat transfer surface and thus the surface condition of the monitor.
These and other objects of the present invention will become apparent upon a consideration of the following drawings and reference to the detailed description which follows.